Reproduced on x8 snakebite.

% ./python.exe 
Python 2.7.3+ (2.7:38a10d0778d2+, Jan 27 2013, 20:05:15) 
[GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
Could not open PYTHONSTARTUP
IOError: [Errno 2] No such file or directory: '/Users/cpython/.pythonrc'
>>> from cStringIO import StringIO
[38179 refs]
>>> f = StringIO()
[38181 refs]
>>> s = 'x' * 2**30
[38183 refs]
>>> f.write(s)
[38183 refs]
>>> f.write(s)
Assertion failed: (oself->pos + l < INT_MAX), function O_cwrite, file /Users/cpython/hg/storchaka/Modules/cStringIO.c, line 421.
zsh: abort      ./python.exe